The issue with Pre-diluted 50/50 is that about a quart or more remains in the engine when doing a flush & refill. You end up with something like 45/55 when using pre-diluted.

That may be true for some vehicles Eddie, but for my 04 Camry V6, it didn't make enough of a difference to change the pre-mixed -34F guarantee. Opening the radiator and both engine banks on the 1MZ_FE V6 completely drains the cooling system.

I always buy 2 gallons of antifreeze if doing anything coolant to my cars. 1 gal pure antifreeze into car/truck. Split the other gallon into empty antifreeze jug with distilled water making 2 gallons 50/50 mix. Top off radiator. -30° to -45° all the time. I then mark the remaining jug "50/50".